A conventional two-stroke engine requires oil to be premixed with the fuel in order to lubricate moving components of the engine. The crankcase has to be sealed as a result. This prevents a two-stroke engine from sharing a crankcase. U.S. Pat. No. 4,450,794 and U.S. Pat. No. 4,791,892, titled “Two-stroke engine”, filed by Roger M. Hall, are good examples of this problem.
A conventional two-stroke engine has transfer ports near bottom dead center which causes some of the fuel to exit the combustion chamber with the exhaust. Complex expansion chambers have helped to solve this problem, but the solution has not work efficiently across the speed range of the engine.
A conventional two-stroke engine has a long piston skirt which often brushes against the cylinder. The reaction force from the piston rod causes the piston to move sideways while the crank shaft is about 45 degree from top dead center.